Traffic signal control system for adjacent intersections

ABSTRACT

A traffic signal control system which includes a parent controller for controlling the traffic signal at a first street intersection and at least one associated controller for controlling the traffic signal at a second street intersection adjacent to the first intersection in a manner associated with the signal control by the parent controller. Normally, the associated controller operates keeping its association with the parent controller. When the association has been broken for one cause or another, the associated controller controls the traffic signal in accordance with a predetermined control pattern of its own independently of the parent controller so as not to cause any confusion to the traffic about the intersections. Means may be provided to indicate whether the associated controller is operating in association with the parent controller or independently thereof.

Elite States atet Todaka et al.

[ 51 ar. 2, W72

[54] TRAFFIC SIGNAL CONTROL SYSTEM FOR ADJACENT INTERSECTIONS [72] Inventors: Hideto Todaka; Hisao Nakatani, both of [21] App]. No.: 628

[30] Foreign Application Priority Data Feb. 16, 1969 Japan ..44/3083 [52] US. Cl ..340/35 [51] Int. Cl. ..G08g 1/085 [58] Field ofSearch ..340/35, 37, 40, 41, 46, Si R PUL 55 Gf/VEPA 70/? 3,500,309 3/1970 Watanabe et a1. ....340/37 3,255,432 6/1966 Lesher ....340/35 3,046,521 7/1962 Cantwell et al. ..340/41 Primary Examiner-Kathleen H. Claffy Assistant Examiner-Randall P. Myers Attorney-Christensen & Sanborn [5 7] ABSTRACT A traffic signal control system which includes a parent controller for controlling the traffic signal at a first street intersection and at least one associated controller for controlling the traffic signal at a second street intersection adjacent to the first intersection in a manner associated with thesignal control by the parent controller. Normally, the associated controller operates keeping its association with the parent controller. When the association has been broken for one cause or another, the associated controller controls the traffic signal in accordance with a predetermined control pattern of its own independently of the parent controller so as not to cause any confusion to the traffic about the intersections. Means may be provided to indicate whether the associated controller is operating in association with the parent controller or independently thereof.

4 Claims, 3 Drawing Figures 4? PARENT 75.

cow/ mm j TRAFFIC SIGNAL CONTROL SYSTEM FOR ADJACENT INTERSECTIONS This invention relates to a traffic signal control system and more particularly to a system for controlling the traffic signals at adjacent street intersections which are associated with each other.

If the traffic signal at a street intersection is controlled in association with the traffic signal control at an adjacent intersection, a smoother traffic flow can be effected than otherwise. In case the distance between the two adjacent intersections is relatively short, vehicles running on the street connecting the two intersections can pass them without being stopped if the traffic signal at one of the intersections is controlled in association with that at the other intersection. Otherwise, that is,

if there is no association between the signal control at the two intersections, the vehicles that passed one of the intersections may have to stop at the other, and if there are many vehicles stopping at one of the intersections, the queue the waiting vehicles form on the street may extend far into the previous intersection so as to cause confusion to the traffic thereabout.

To control the traffic signals at adjacent street intersections in an associated manner, a traffic-actuated signal controller (to be referred to as the parent controller) is provided to control the signal lights at one of the adjacent intersections (to be referred to as the parent intersection), and associated with the parent controller is a signal controller (to be referred to as the associated controller) to control the signal lights at the adjacent street intersection (to be referred to as the associated intersection). Normally, the associated controller receives the association signals produced by the parent controller and controls its signal lights in accordance with the received association signals. The association signals are produced when the phases or steps of the traffic signal cycle of the parent controller are changed, and upon receipt of an association signal the associated controller operates to change the phases or steps of the signal cycle at the associated intersection.

Under the normal condition that the parent and associated controllers are operating in the above-mentioned associated manner, when the association signal has not been produced or the associated controller has been disabled from receiving the association signal, the association between the two controllers has been broken so that the signal control at the associated intersection can no longer be performed in association with the signal control at the parent intersection, with resulting confusion to the traffic on the streets around the intersections.

Accordingly, it is one object of the invention to provide a traffic signal control system wherein a parent controller controls the traffic signal at one intersection and at least one other controller operatively associated with said parent controller controls the traffic signal at a street intersection adjacent to said one intersection.

Another object of the invention is to improve the manner of association between the parent and associated controllers.

Still another object of the invention is to provide such a traffic signal control system as aforesaid wherein when the associated controller has not received the association signal from the parent controller for one cause or another, the associated controller controls its traffic signal in accordance with a predetermined control pattern ofits own independently of the parent controller thereby avoiding any traffic confusion about the intersection.

In accordance with the invention, the associated controller controls the traffic signal at the associated intersection in accordance with a number of phases or steps predetermined for the associated controller, and among these steps those which must be associated with the corresponding steps of the parent controller are controlled or changed by the association signals which the parent controller produces and alternatively by the step signals which the associated controller provides. Normall). that is, while the association between the parent and associated controllers is maintained, the association signals and not the step signals change the steps of the signal cycle of the associated controller. However, when the associated controller has not received any succeeding association signal for a predetermined period of time after the preceding association signal was received, the step signal takes over to change the steps of the signal cycle. Thus, when the association signals have not been received by the associated controller, the step signals provide a fail-safe function and automatically change the steps of the signal cycle of the associated controller.

It is desirable that the supervisor of the traffic signal control system should know whether the associated controller is now operating in association with the parent controller or independently therefrom.

An additional object of the invention is therefore to provide such a traffic signal control system as aforesaid which is capable of indicating whether or not the association is now being maintained between the parent and associated controllers.

The invention with its above and other objects, features and advantages will be better understood from the following detailed description of some preferred embodiments thereof with reference to the accompanying drawings, wherein;

FIG. 1 is a schematic top plan view oftwo adjacent street intersections to which the system of the invention is applied;

FIG. 2 is a time chart showing the sequential illuminating conditions of the signal lights in FIG. 1 in the different phases and steps of one signal cycle; and

FIG. 3 is an electrical block diagram of the system of the invention.

Referring now in detail to the drawing, first to FIG. 1, there is shown a major street 1 which crosses two minor streets 2a and 2b to form two street intersections l0 and 20, respectively. It is assumed that the traffic signal at the intersection 20 is normally controlled in accordance with the signal control at the intersection 10. The intersections l0 and 20 will hereinafter be referred to as the parent and associated intersections, respectively. In the illustrated embodiment, there is a single associated controller, but the system of the invention may include as many associated controllers as there are intersections adjacent to the parent intersection.

The parent intersection 10 is provided with two signals 11 facing the major street 1 and two signals 12 facing the minor street 20. The signals 11 and 12 are controlled by a traffic-actuated controller 13 to be referred to as the parent controller hereinafter. It is assumed that two-phase control is employed. Any suitable conventional traffic-actuated controller may be used as the parent controller, provided that there is provided means for producing association signals to be applied to the associated controller. The structure and operation of such a conventional traffic-actuated signal controller are so well known that no further description thereof will be required.

The associated intersection 20 is provided with two signals 21 facing the major street 1 and two signals 22 facing the minor street 2b. These signals are controlled by an associated controller 23. It is assumed that here, too, two phase control is employed just as at the parent intersection 10. As shown in the time chart of FIG. 2, at the first step of the signal cycle, the parent controller 13 illuminates the green light 1G of the signal 11 and at the same time the red light 2R of the signal 12. The time of duration of the green signal 1G is automatically determined between the predetermined minimum and maximum periods of time by the parent controller 13 in accordance with the traffic condition around the intersection 10. When the green signal 1G terminates, the second step of the signal cycle comes so that the yellow light lY' of the signal 11 is illuminated. At this time the parent controller 13 produces a first association signal S1. The yellow signal lY' lasts for a predetermined period of time, and upon termination of the signal lY' the third step is reached so that the signals 11 and 12 are rendered red IR and green 2G, respectively. The period of time of the green signal 2G is automatically determined between the predetermined minimum and maximum in accordance with the traffic condition around the intersection 10 just as in the case of the green signal 1G. Presently, the third step ends and the fourth steps commences, whereupon the signal 12 is changed from green 2G to yellow 2Y. At the same time the parent controller 13 produces a second association signal S2. The yellow Signal 2Y lasts for a predetermined period of time, upon lapse of which one signal cycle has ended and the next signal cycle begins with the first step again.

Under the condition that the normal association is maintained between the operations of the parent and associated controllers 13 and 23, the latter controller operates in the following manner: In the first step, the signals 21 and 22 are green 16 and red 2R, respectively. When the first association signal S1 comes, the second step begins changing the signal 21 to yellow lY. The yellow signal lasts for a predetermined period of time, upon lapse of which the third step comes changing the signals 21 and 22 to red IR and green 2G, respectively. During the green signal indication 2G the second association signal 52 arrives to start the fourth step so that the signal 22 is changed to yellow 2Y. The yellow signal 2Y lasts for a predetermined period of time until the first step is resumed to start the next signal cycle.

If the controller 23 does not receive the association signals S1 and S2, the signals 21 and 22 will continue their respective green indications 1G and 26 throughout the whole signal cycle, with resulting confusion to the traffic about the intersectlon.

The system of the invention is so arranged that even when the associated controller 23 does not receive the association signal S1 and/or S2, the green signal 1G or 20 will never continue throughout the signal cycle but terminate when it should. To this end, the associated controller 23 is provided with means for presetting the green times 16 and 2G independently of the parent controller, so that if the next association signal S1 or 52 has not arrived within the preset green time 16 or 20, the associated controller breaks its association with the parent controller and independently operates to advance the signal cycle from the first or third step to the second or fourth step upon termination of the preset green time or 26.

The above arrangement ofthe associated controller that the green times 10 and 20 can be preset independently of the association signals has another advantage as follows: It is in some cases required that the green time 20 should end earlier than it normally is caused to end by the association signal 52 in order to make the green time 10 the longer. To meet the requirement, the green time 20 may be preset to such a length as to terminate before the association signal S2 is produced, so that the green signal 1G begins earlier and consequently lasts longer than otherwise to clear the traffic on the street 1 through the intersection 20.

Now turning to FIG. 3, there is shown a pulse generator 30 designed to produce, say, one pulse per second. The pulses produced by the generator 30 are counted by a pulse counter 31 having a plurality of output terminals 1, 2, 4, ....2". A step time presetting device 32 receives as one input the outputs from the pulse counter 31 and as the other input the output on the terminals 1, 2, 3 and 4 of a quaternary pulse counter 33. The counter 33 counts the output pulses from a monostable multivibrator 34 and steps forward shifting its output succes sively from the output terminals 1 through 4. The outputs on the terminals 1, 2, 3 and 4 of the counter 33 correspond to the first, second, third and fourth steps of one signal cycle of the associated controller 23, respectively.

The signal on the output line 1 of the counter 33 illuminates the lights 16 and 2R; the signal on the line 2, the lights 1Y and 2R; the signal on the line 3, the lights 26 and IR; and finally the signal on the output line 4, the lights 2Y and IR.

The step time presetting device 32 comprises four matrices 51-54 of the pinboard type. These matrices 51-54 preset the periods of time of the first to fourth steps, respectively, by inserting a pin into some of the pinholes H in each matrix. The outputs from the matrices together with the outputs from the counter 33 are applied to AND circuits 55-58, respectively. When two signals coincide, the circuits 55-58 produce an output on lines T1, T2, T3 and T4, respectively. Therefore, the output signals T1-T4l are produced when the preset periods of time of the first-fourth steps of the signal cycle have elapsed, respectively. The signals T1-T4 are applied to an OR element 35, the output from which is applied to an OR element 39. The output from the OR element 39 triggers the monostable multivibrator 34 to produce an output pulse. As previously mentioned, the output pulse from the multivibrator 34 causes the pulse counter 33 to step forward and at the same time resets the counter 31. Thus, the counter 31 is reset every time the counter 33 makes one forward step.

The previously mentioned association signals 51 and 52 produced by the parent controller 13 are applied as one input to AND elements 36 and 37, respectively. The signals on the output lines 1 and 3 of the counter 33 are applied as the other input to the AND elements 36 and 37, respectively. Therefore, when the signal on the output line 1 of the counter 33 coincides with the signal S1, the AND element 36 produces an output, which is applied through the OR elements 38 and 39 and the monostable circuit 34 to cause the counter 33 to shift its output onto the next output line 2 thereby starting the second step of the signal cycle. In like manner, when the signal on the output line 3 of the counter 33 coincides with the association signal S2, the output is shifted onto the line 4 thereby starting the fourth step ofthe signal cycle.

It is assumed that the period of time the first step lasts, that is, the length of the green time 16 as preset by the matrix 51 and the period of time the third step lasts, that is, the length of the green time 26 as preset by the matrix 53 are longer than the maximum lengths of the green times 16 and 20 of the parent controller, respectively.

Under normal condition, that is, when the association is maintained between the parent and associated controllers, in the first step the association signal S1 is produced before the first step signal T1 is produced because the green time 10 as set by the matrix 51 is longer than the maximum green time 16. When the association signal 51 comes coinciding with the output on the line 1 of the counter 33, the AND element 36 produces an output to trigger the monostable multivibrator 34 through the OR elements 38 and 39. The output from the multivibrator 34 resets the counter 31 and at the same time causes the counter 33 to shift its output onto the terminal 2 thereby starting the second step of the signal cycle.

The period of time the second step lasts is preset by the matrix 52 and upon lapse of that preset period of time, the second step signal T2 is produced to reset the counter 31 and causes the counter 33 to make a forward step thereby starting the third step of the signal cycle. At the end of the third step (the green time 2G), the second association signal S2 is produced before the production of the third step signal T3, because the time preset by the matrix 53 is longer than the maximum green time 26. The signal S2 coincides with the output on the third terminal 3 of the counter 33, whereupon the AND element 37 produces an output, which triggers the monostable multivibrator 34 through the OR elements 38 and 39. The output from the multivibrator 34 resets the counter 31 and at the same time causes the counter 33 to shift its output onto the fourth terminal 4 thereby starting the fourth step of the signal cycle.

The period of time of the fourth step is preset by the matrix 54, upon lapse of which the step signal T4 is produced to trigger the monostable multivibrator 34, so that the counter 31 is reset and the counter 33 has its output shifted back to the terminal 1 for commencement of the first step of the next signal cycle.

The above operation is repeated so long as the normal association is maintained between the operations of the parent and associated controllers. Suppose, however, that for one cause or another the association signals 51 and S2 are not applied to the AND elements 36 and 37 during one signal cycle. Then all of the step signals Tl-T4 are applied to the OR element 39. This means that the counter 33 is caused by these step signals alone to shift its output, and that the periods of time the first-fourth steps of the signal cycle are those determined by the matrixes 51-54, respectively, so that a fixedcycle signal control at the associated intersection is conducted by the associated controller 23 independently of the parent controller 13.

it is desired in some cases that the length of the third step, that is, the green time 26 as set by the step time presetting device 32 is shorter than the maximum green time 26 of the parent controller 13. To meet the requirement, the length of the first step, that is, the green time 16 as set by the device 32 is taken into account. That is, the green time 16 is set to a length longer than the sum of the maximum green time 16 and the maximum green time 20 minus the green time 26. With this arrangement, in the third step the step signal T3 is produced before the second association signal 52 is produced, so that the signal T3 causes the counter 33 to step forward thereby bringing in the fourth step of the signal cycle. Thus, the green time 26 has been made shorter than the green time 26.

When the time set for the fourth step has elapsed, the first step of the next signal cycle begins. In the first step, since the green signal 16 is set to a sufficiently long time, prior to the production of the step signal T1 the association signal S1 is produced to advance the signal cycle from the first onto the second step thereof. Therefore, it may be said that the association between the parent and associated controllers is still maintained through the function of the association signal S1.

in the above description, while the normal association is maintained between the parent and associated controllers, the instant the green time has passed the association signal S1 terminates the green time 10 and the instant the green time 20' has passed the signal S2 terminates the green time 2G. In other words, no offset is provided between the operations of the parent and associated controllers 13 and 23. If desired, an offset can be provided with ease by inserting a delay element 61, 62 between the parent controller 13 and each of the AND elements 36 and 37 of the associated controller 23, so that the signals Sland S2 are delayed by the elements 61 and 62, respectively. The lengths of the offsets are determined by the delay times provided by the elements 61 and 62.

It is desirable to know whether the association is maintained between the two controllers l3 and 23 or the associated controller 23 is operating independently of the parent controller 13. To this end the outputs from the AND elements 36 and 37 are applied through the OR element 38 to a monostable multivibrator 41, the output from which is applied as a set input to a flip-flop 43. The output on the second and fourth lines 2 and 4 of the pulse counter 33 is applied through an OR element 40 to a differentiator 42, the output from which is applied as a reset input to the flip-flop 43. The flip-flop 43 is such that while the output from the monostable multivibrator 41 is being applied as a set input to the flip-flop 43, it remains set even when the differentiator 42 applies a reset input to the flip-flop. The reset output from the flip-flop 43 illuminates a lamp 44. When the flip-flop remains set, however, the lamp is off and when the flipflop is reset, the lamp 44 is turned on.

Suppose that the associated controller 23 is operating independently of the parent controller 13. The AND elements 36 and 37 produce no output, so that the flip-flop 43 receives no set input. On the other hand, as the counter 33 steps forward, its output on the lines 2 and 4 resets the flip-flop thereby illuminating the lamp 44.

When the two controllers l3 and 23 are operating in association, the signal S1 at the end of the first step of the signal cycle causes the AND element 36 to produce an output, which causes the flip-flop 43 to be set. At the same time, the pulse counter 33 shifts its output onto the next output line 2, and this output is applied to the flip-flop 43. At this time, however, the output from the monostable multivibrator 41 continues to be applied to the set input of the flip-flop 43, so that despite the reset input thereto the flip-flop is not reset but remains set and consequently the lamp 44 is kept turned off. The same is true when the next association signal S2 comes. The lamp 44 may be replaced by any other suitable indicator.

What we claim is:

1, A traffic signal control system comprising: a first controller for controlling the traffic signal at a first street intersection; a second controller for controlling the traffic signal at a second intersection adjacent to said first intersection; said first controller producing an association signal for a change in phase of the traffic signal at said first intersection; said second controller comprising means for presetting the period of time each of the phases of one signal cycle of the traffic signal at said second intersection lasts and producing a phase change signal upon lapse of each said preset phase time, and phase advancing means operable in response to either said association signal or said phase change signal, whichever occurs first, to change the phase of said second traffic signal.

2. The system of claim 1, wherein said phase advancing means comprises a pulse counter, first circuit means controlled by the output from said pulse counter to produce an output upon receipt of each said association signal only if said association signal occurs before its corresponding phase change signal and second circuit means causing said pulse counter to step forward in response to either said phase change signal or said output signal from said first circuit means.

3. The system of claim 1, further including means for delaying said association signal to provide an offset between the end of the green time of said first controller and the actuation of said phase advancing means.

4. The system of claim 1, further including means for indicating whether control of said phase advancing means in said second controller is being effected by said association signals or by said phase change signals. 

1. A traffic signal control system comprising: a first controller for controlling the traffic signal at a first street intersection; a second controller for controlling the traffic signal at a second intersection adjacent to said first intersection; said first controller producing an association signal for a change in phase of the traffic signal at said first intersection; said second controller comprising means for presetting the period of time each of the pHases of one signal cycle of the traffic signal at said second intersection lasts and producing a phase change signal upon lapse of each said preset phase time, and phase advancing means operable in response to either said association signal or said phase change signal, whichever occurs first, to change the phase of said second traffic signal.
 2. The system of claim 1, wherein said phase advancing means comprises a pulse counter, first circuit means controlled by the output from said pulse counter to produce an output upon receipt of each said association signal only if said association signal occurs before its corresponding phase change signal and second circuit means causing said pulse counter to step forward in response to either said phase change signal or said output signal from said first circuit means.
 3. The system of claim 1, further including means for delaying said association signal to provide an offset between the end of the green time of said first controller and the actuation of said phase advancing means.
 4. The system of claim 1, further including means for indicating whether control of said phase advancing means in said second controller is being effected by said association signals or by said phase change signals. 